End zone retardation control system



Dec. 12, l

K. SCHiEBELER 2,183,409

END ZONE RETARDATION CONTROL SYSTEM Filed Feb. 5, 1938 I6 3o 6'0 ea so100 Lergth of slow down pat/2 in percentage, of /ength of end zone.

Fig. 3.

Braking torque a: is

Inventor Hi Attorney.

Patented Dec. 12, 1939 2,183,4taa

UNITED STATES PATENT OFFlCE END ZONE RETARDATION CONTROL SYSTEM KarlSchiebeler, Berlin-Gharlottenburg, Germany, assignor to General ElectricCompany, a corporation of New York Application February 5, 1938, SerialNo. 188,990 In Germany February 15, 1937 Claims. (Cl. 188182) Thisinvention relates to control systems, more to eiTeet a ry rapid releaseof the brake and particularly to systems fo t ll h b kreconnection ofthe motor. The drive when uning of traveling cranes, loading bridges andtheir braked or braked an inconsiderable amount, may trolley carriagesand the like apparat and it thus travel through the end zone withsufiicient 5 has for an object the provision of a simple, r speed andforce to demolish the bufiers, pass off liable, and improved system ofthis character. iThe end of the track, and Wreck itself- In the case ofelectrically operated driving Accordingly, an object of the P tillVengears with large m parts, Such fo examtion is the provision ofmeans for eliminating the pie as rapidly traveling crabs and cranes orloadforegoing disadvantages.

v ing bridges, etc., retardation braking is neces- In Carrying einvention into effect in One Q sary. form thereof, electro-hydraulicbrake operating In the free running zone of the track, this means areprovided which are regulated in deretardation is usually effected bymeans of elecp e p n h p d and the length f the trical braking under thecontrol of the operator. end Zone to he traveled In the end Zone,however, the control may be For a better and more complete understandingtaken away from the operator and effected auto- 0f the invention,reference should now be had matically in order to prevent damage to theapto the following specification and to the accomparatus. This isusually accomplished by ar- Denying drawing in Which Fig. 1 is a simprangin the control so that a limit switch is acschematic diagram of anembodiment of the 20. tuated to disconnect the motor and apply theVention, and Figs. 2 and 3 e Char s Of cheraebrake as the apparatusenters the end zone. The teristie Curves Which explain theOperationlength of the end zone is so chosen that if the Referring now tthe draw n a wheel In of apparatus enters the end zone at maximum speed,the traveling gear 111115 On a l"e11 (I101? w the brake will bring theapparatus to a stop at a d is connected through Suitable driving thehorrors arranged at the end of the end zone. nections t0 h driving motor(not w A Since the kinetic energy stored in the apparatus brake m II smechanically Connected the which must be dissipated by the brake varieswith Wheel 1 Brake O S 2 are a y Set the square of the speed, the lengthof the slow against e d y Suitable eans Such as down path also varieswith the square of the p g l3, and the braking force of e Sh0e$ speed.Consequently, if the apparatus enters against t drum s' ed y an e 0hy-30 the end zone at low speed, the length of the slow draulic d ce II!when the apparatus is n e down path is greatly shortened and the drivingnd z A h y Suitable e1 r0hydr gear is brought to standstill prematurelyand at C brake Operating means y be utilized, a a distance from thebuffers that varies inversely ce Such as the eleetrwhydreulie Operatorwith the square of the speed at which the ap- Closed in United statesPatent 2,035,793

paratus entered the end zone. Therefore, in Driesch is preferred. Th s dv e C p s s a order to complete the movement of the appacylinder l-iawhich contains a liquid such as oil,

ratus to the buliers at the end of the end zone, a movable piston, and aliqu d impeller driven by it is necessary to reenergize the drivingmotor. m s 01" an electric motel" The Piston iS For this purpose, it isnecessary to provide the connected through push rods l6 and H to the 40master switch with one or more switching posibrake shoe operating leverI8.

tions in order to provide for release of the brake When the motor i5 isdeenergized, the imand reconnection of the motor to the source forpeller is at rest and no fluid pressure is derotation in the samedirection as previously, to veloped in the cylinder [4. On the otherhand,

complete the run to the end buffers after the rewhen the motor I5 isenergized, a fluid pressure 45 sponse of the end zone entrance limitswitch. is developed and the piston is raised and applies This isusually accomplished by arranging the a force to move the brakeoperating lever l8 control so that when the master switch is in oneagainst the force of the spring l3 in a direction of the low speedpositions, the end zone entrance to release the brake shoes. Themagnitude of limit switch is rendered ineffective. With such thisreleasing force depends upon the fluid pres- 50 an arrangement it ispossible for the operator sure exerted against the piston which in turndeby a switching of the master switch to pends upon the speed of themotor l5. Thus by one of these positions as the apparatus enters thevarying the speed of motor I5, the braking force and zone to trick thecontrol and prevent disconcan be regulated.

nection and application of the brake or at least The armature ofimpeller motor [5 is con- 55 ill nected to a suitable source of supplyrepresented by supply lines E9 in series relationship with the armatureof a control dynamo-electric machine 2% which is mechanically connectedto the axle of wheel H3. Machine 26 is provided with a self-excitedfield winding 2i and. a separately excited field winding 22 ofrelatively weak excitation. The armature of machine Pill is so connectedin the series circuit that its Voltage adds to the counter-voltage ofmotor l and opposes the voltage of source 19. A limit device 23 isarranged at the entrance to the end zone, and the buifer is mounted atthe end of the end zone. A suitable switching device 25, illustrated. asa snap action, over-center switch cooperates with limit device 23 toconnect the armature of control machine 29 in series relationshipbetween the armature of motor iii and the source when the apparatusenters the end zone. Similarly, a suitable switching device 26cooperates with actuating devices El and 28 to short-circuit resistor 2ain the self-excited field circuit of control machine 2d so as to varyits voltage in accordance with the position of the apparatus in the endzone, 1. e., in accordance with the amount of the end zone remaining tobe traveled.

Switch 25 is illustrated in the position which it occupies after theapparatus entered the end zone. Prior to entrance into the end zone,switch 25 occupies the position shown in dotted lines and connects thearmature of impeller motor l5 directly to the source l9, as a result ofwhich the motor i5 operates at maximum speed, and maximum fluid pressureis exerted against the piston to effect complete release of the brake.As the apparatus enters the end zone, switch 25 engages limit device 23and is snapped from its dotted line position to its full line positionas shown. It is usual, as stated in the foregoing,

to arrange the control so that the limit switch 25 disconnects thedriving motor from the source and sets the brake as the apparatus entersthe end zone. Since this in itself is not a novel feature, it is notillustrated in the drawing.

The greater the speed of the apparatus the greater will be the voltageof the control machine 2d, and therefore the smaller will be the voltageapplied to motor l5, (since only the difference between line voltage andthe voltage of machine Bil is applied to motor l5) and the smaller willbe the lifting force of the electro-hydraulic mechanism and the greaterwill be the braking force of the shoes !2 against drum H. On the otherhand, with the speed of the apparatus becoming lower, the lifting forceof the electro-hydraulic mechanism will increase because the voltage ofmachine 2% is correspondingly decreased, and the braking force iscorrespondingly decreased. In other words, the braking force of themechanical brake is graduated in accordance with the speed of theapparatus when in the end zone.

It will readily be seen that this arrangement results in a longerslowing down path as compared with the slowing down path of apparatushaving an unregulated brake which is fully applied upon entering the endzone and remains fully applied because in the improved system, thebraking energy decreases with the decrease in speed. If the apparatusenters the end zone at low speed, as is frequently the case whentraveling over short distances prior to entering the end zone, then acorrespondingly reduced braking force is effective from the instant ofentering the end zone, which results in a correspondingly smoothbraking, so that the driving gear no longer prematurely comes to a stopas heretofore, but in this case also can run as far as the buffers.These conditions are represented in Fig. 2, in which curves 30, 3|, and32 illustrate the relationship between speed of the apparatus enteringthe end zone and length of the slow down path in percentage of length ofthe end zone when braking by the prior art method, and curves 33, S4 and35 represent the same relationships when braking by the improved methodof the invention. It is to be observed that when constant full brakingtorque is used, a slight decrease in speed of entering the end zoneresults in greatly shortening the slow down path; the driving gear stopsbefore traveling half the length of the end zone, and the driving motormust be reenergized in order to travel to the end of the end zone. Withthe improved arrangement of the invention, on the other hand, braking atless than full speed is effected with less braking torque and therebythe same slowing down path is obtained as in the case of full speed.

The arrangements previously described would be entirely satisfactory ifthe braking torque were directly proportioned to the speed of theapparatus from 100% speed to zero speed. Such, however, is not the case.The entire range of lifting force of the electro-hydraulic liftingapparatus, and consequently the entire range of the braking torque lieswithin a much narrower speed range, approximately between 70-90% of thespeed at which the brake is fully released. Fig. 3 shows how thisproblem is solved. On curve 30 in Fig. 2 each point in the end zonecorresponds to a predetermined speed of the apparatus.

At a point about half way in the end zone corresponding to a speed ofapproximately 75% to 80% of full speed, the retardation switch 26engages the stop Zla and is actuated from the full line position inwhich it is shown to the first dotted line position in which it shortcircuits one section of resistor 29 thereby to increase the excitationof control machine 20. This increases the voltage of machine 29 anddecreases the speed of impeller motor 55, thereby reducing the brakereleasing force of the electro-hydraulic mechanism and again increasingthe braking torque applied to the drum. At a further point in the endzone the switch 26 engages stop 28a and the foregoing action isrepeated. These operations are represented by the curve 36 in Fig. 3. Ifthe speed of the impeller motor had not been reduced at theseintermediate points the braking torque would have been reduced to zerobefore the apparatus had traversed half the length of the end zone.

As the apparatus approaches the buffer at low speed, switch 25 passesover actuating device 38 by rotating the upper movable member in acounterclockwise position against the force of the positioning spring.When the apparatus has passed, the spring returns the movable member tothe position in which it is shown. The apparatus. finally comes to restagainst the buffer. When operations in the end zone are completed, themaster switch (not shown) is actuated to energize the crane drivingmotor in the reverse direction. As the apparatus leaves the buifer,switch 25 engages actuating device 38. Since the upper movable member ofthis device cannot rotate in a clockwise direction, the switch isactuated from the position in which it is shown to the dotted lineposition in which motor !5 is connected directly to the supply sourceand the brake is fully released.

If the apparatus enters the end zone at a lower speed, the operation isrepresented by curve 31 in Fig. 3.

When entering the end zone at low speeds, the brake is fully releasedand produces no braking torque. After the driving motor is disconnected,only the frictional resistances of the driving gear are effective forbraking, so that the end zone is traversed with correspondingly lessreduction in speed.

Although a direct current control system is disclosed for the purpose ofillustration, it will be understood that the invention includesalternating current systems in which the impeller of theelectro-hydraulic mechanism is driven by an alternating current motorconnected to the source through a frequency converter mechanicallyconnected to the shaft of the driving gear through a variable speedtransmission which is adjusted through the retardation switch lever. Inthe case of three-phase current drives a direct current control machinecan also be utilized and this can be operated through dry rectifiers orother converters from the three-phase system as described in connectionwith the system of Fig. 1.

The effect of the braking can be obtained without jerking and sliding onmoist rails prevented if the brake rods are not rigidly coupled with theelectro-hydraulic release, but mounted between two springs acting inopposition to each other. Thereby a gradual increase of the brakingenergy from zero to the maximum value is obtained.

If the apparatus should come to rest prematurely because of entering theend zone at low speed, the driving motor can be reconnected to thesource by operation of the master switch. This is no longer adisadvantage nor dangerous expedient because the speed of the drivingmotor cannot exceed the permissible value allowed by the mechanicalbrake and its control.

Although in accordance with the provision of the patent statutes, theprinciple of this invention has been explained together with what is nowconsidered to be the best mode of applying the principle, it will beunderstood that the apparatus and connections shown are merelyillustrative and that the invention is not limited thereto sincealterations and modifications will readily suggest themselves to personsskilled in the art without departing from the spirit of the invention orfrom the scope of the annexed claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. An end zone retardation control system for traveling cranes, loadingbridges and the like apparatus comprising a mechanical brake for saidapparatus, electro-hydraulic operating means for said brake, meansresponsive to the speed of said apparatus for controlling said operatingmeans and means independent of said speed responsive means andautomatically operable in response to the position of said apparatusWithin the end zone for modifying the control or" said brake operatingmeans.

2. An end zone retardation control system for traveling cranes, loadingbridges and the like apparatus comprising a mechanical brake for saidapparatus, electro-hydraulic operating means for said brake, meansresponsive to a decrease in the speed of said apparatus for controllingsaid operating means to decrease the braking torque of said brake, andmeans automatically responsive to the position of said apparatus in theend zone for modifying the control of said operating means to increasesaid braking torque at predetermined positions in said end zone.

3. An end zone retardation control system for traveling cranes, loadingbridges and the like apparatus comprising a mechanical brake for saidapparatus, electro-hydraulic operating means for said brake, a controldynamo electric machine driven by said apparatus at a speed proportionalto the speed of said apparatus for controlling said operating means tovary the braking torque of said brake in accordance with the speed ofsaid apparatus, and means for modifying the control of said operatingmeans in accordance with the position of said apparatus in the end zone.

4. An end zone retardation control system for traveling cranes, loadingbridges and the like apparatus comprising a mechanical brake for saidapparatus, electro-hydraulic operating means for said brake, a controldynamo electric machine driven by said apparatus at a speed proportionalto the speed of said apparatus for controlling said operating means tovary the braking torque of said brake in accordance with the speed ofsaid apparatus, means for modifying the control of said operating meansin accordance with the position of said apparatus in the end zonecomprising means for controlling the eX- citation of said controlmachine to increase the braking torque at predetermined points in theend zone.

5. An end zone retardation control system for traveling cranes, loadingbridges, and the like apparatus, comprising in combination, saidapparatus, a mechanical brake for said apparatus, electric meansincluding a motor for operating said brake, a source of supply forenergizing said motor, a control dynamo electric machine driven by saidapparatus at a speed proportional to the speed of said apparatus, andmeans responsive to the position of said apparatus for connecting saiddynamo electric machine in circuit with said motor and said source ofsupply therefor to vary the speed of said motor in accordance with thespeed of said dynamo electric machine and thereby control the brakingtorque of said brake in accordance with the speed of said apparatus.

KARL SCI-IIEBELER.

